Human corneal dystrophies and degenerations which have been clinically documented are studied as keratoplasty specimens with histochemical stains, scanning and transmission electron microscopy, and immunologic techniques in an attempt to elucidate pathogenetic mechanisms. This approach has provided insight into cell-to-cell relationships in the normal and diseased states. In patients with primary and recurrent macular corneal dystrophy, intercellular and extracellular accumulation of fibrillogranular material was observed in the corneal stroma, Descemet's membrane, and corneal endothelium. The presence and production of collagen, glycoconjugates, and collagenase have been investigated with immunofluorescent electrophoretic, and chromatographic methods. The lectin binding patterns were compared in corneas from patients with macular dystrophy and control. The characterization of amyloid in lattice corneal dystrophy and corneal amyloid degeneration was performed using immunohistochemical stains and biochemical analysis. Lack of AA reactivity was observed in corneal amyloid deposits. Keratoplasty specimens from granular corneal dystrophy and controls were examined by combinations of immunohistological stains, transmission electron microscopy, and SDS gel electrophoresis. In granular dystrophy, the deposits consisted of phospholipid with microfibrillar protein at the edges. Corneal buttons from patients with Fuchs' dystrophy had varying degrees of clinical edema measured in most cases by preoperative optical ultrasonic pachymetry. Histologically, marked thickening of Descemet's membrane and abnormal corneal endothelium corresponded to areas of severe clinical edema and were usually located in the central and paracentral regions. Clinical edema was not present unless accompanied by marked thickening of Descemet's membrane with multiple guttata and attenuation of corneal endothelium. The peripheral cornea was relatively clear clinically and showed minimal histologic changes.